Axial flow air turbines can have various uses. One significant use is in an air drive unit incorporated in modern day wide-body aircraft such as the Boeing 747, 767 and 777 aircraft to augment engine driven hydraulic pumps during peak demand periods. The air drive unit also serves to provide hydraulic power during emergency conditions when one or more of the primary engine driven hydraulic pumps are inoperative. An air drive unit includes a turbine gearbox assembly, a modulating valve, a hydraulic pump, and other ancillary components such as a muffler, ducting, controller, and clamps. The turbine gearbox assembly contains the axial flow air turbine, inlet volute, nozzle, exhaust diffuser, gearbox assembly, and hydraulic pump interface.
In operation, engine bleed air flows through the inlet volute and turbine nozzle and drives the axial flow turbine. The turbine power generated by the engine bleed air is transmitted to the hydraulic pump interface through the gearbox. The gearbox allows the turbine to rotate at a much higher speed than the hydraulic pump, thus maximizing turbine efficiency without adversely effecting pump life. It is generally desirable to operate the turbine at nearly constant speed during all operational conditions. Since the engine bleed air pressure and hydraulic load vary during operation, a method for controlling the flow entering the turbine is required for stable, constant speed operation. Flow control currently is typically exerted in one of the following two ways:
1. Bleed air is metered by a modulating valve located upstream of the air turbine inlet volute. This system of control typically utilizes a fixed area nozzle to accelerate air into the axial flow turbine.
2. Bleed air is modulated by variable inlet guide vanes which serve as a variable geometry nozzle to accelerate air into the axial flow turbine. With this method the turbine speed is maintained constant by varying the nozzle area under varying power conditions.
The first system, utilizing a modulating valve, is far simpler than the second, utilizing variable inlet guide vanes. Only one moving part is typically utilized in an air modulating valve, whereas variable inlet guide vanes necessitate synchronized rotation of every nozzle vane. In addition to the actuating mechanism, each of the typically more than twenty nozzle vanes in a variable inlet guide vane system must contain suitable bearing surfaces, a timing gear, and precision shafts. Consequently initial cost of a system employing variable geometry is far greater than that of a system employing a modulating valve. In addition, the reliability of a variable inlet guide vane system is inherently lower than systems employing a modulating valve for turbine control due to the increased complexity and the increased number of parts.
The benefit of using a variable inlet guide vane system is reduced air consumption at normal operating conditions, especially at the sea level take-off condition. At this condition, maximum power must be delivered by the air drive unit to quickly retract the landing gear. At the same time, maximum engine thrust is required, and maximum engine bleed pressure is available. Since engine bleed air is taken directly from the engine compressor, which reduces the available engine thrust, it is desirable to minimize the bleed air consumption when maximum engine thrust is required.
The air drive unit can produce the required power at the sea level take-off condition by utilizing the high pressure supply air and using a small nozzle area to accelerate the flow into the turbine. This approach minimizes the required engine bleed flow rate, and is thus the most desirable in terms of engine performance. However, a primary role of air drive units is to provide power during emergency conditions. The emergency requirement that typically sizes the machine is a low pressure (typically 25%-50% of the sea level take-off pressure), high power condition. To produce high power at low pressure requires a large nozzle area and consequently high bleed air flow consumption.
Since the nozzle area in a variable inlet guide vane system can be controlled, the area is minimized for the sea level take-off condition to minimize bleed air consumption, and maximized for low pressure emergency conditions to produce the required power. Systems employing a modulating valve, however, normally use a fixed area nozzle. Since the low pressure emergency condition requires the largest nozzle area of all operational conditions, the fixed nozzle area in these systems is sized for this requirement. As a result, during the sea level take-off condition, and most operational conditions, systems employing a modulating valve for flow control have a much larger nozzle area than required. As a result, these systems consume more bleed air than similar variable inlet guide vane systems at the same condition (up to 40% more at the sea level take-off condition).
The inlet nozzle air control apparatus invention for an axial flow air turbine solves the problem of excessive air consumption in fixed nozzle systems without the added complexity and cost of a variable inlet guide vane system. Use of the inlet nozzle air control apparatus invention results in optimal flow consumption at two design points, as opposed to the single optimal design point of a fixed area nozzle, and performance equivalent to that of a variable inlet guide vane system at those design points, with far less complexity since only one additional moving part is required. The reduced complexity means improved reliability with equivalent performance. This invention can be successfully employed whenever optimal performance of an axial flow turbine is required at more than one operating condition.
The inlet nozzle air control apparatus invention offers automatic (self actuated) optimal nozzle area selection, with minimal complexity. This allows an axial flow turbine to operate optimally, thus reducing air flow consumption, at more than one design condition. This inlet nozzle air control apparatus invention allows multi point design optimization at a fraction of the cost of variable inlet guide vane systems, and with far greater reliability. Thus, simplicity and cost comparable to the fixed nozzle, modulating valve controlled system, and performance comparable to the complex variable inlet guide vanes controlled system is achieved using the inlet nozzle air control apparatus invention.
This invention relates to axial flow turbines and more particularly to axial flow turbines having increased flexibility.
Accordingly, it is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine.
It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that increases the flexibility of the axial flow turbine.
It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that permits optimal performance of the axial flow turbine.
It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that permits optimal performance of the axial flow turbine at more than one turbine operating condition.
It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that permits optimal performance of the axial flow turbine at a plurality of turbine operating design points.
It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that permits optimal performance of the axial flow turbine at at least two turbine operating design points.
It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that reduces air consumption.
It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that permits a reduced nozzle area.
It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that is reliable.
It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that has few parts.
It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that has only one moving part.
It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that is simple in its operation.
It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that is easy to operate.
It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that has reduced complexity.
It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that has reduced weight.
It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that has reduced maintenance.
It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that is easy to manufacture.
It is an object of the invention to provide inlet nozzle air control apparatus for an axial flow turbine that has a low manufacturing cost.
These and other objects will be apparent from the invention that includes inlet nozzle air control apparatus for an axial flow air turbine having an inlet nozzle for air entering the turbine and an associated turbine inlet housing for channeling air to the inlet nozzle comprising means for at least partially blocking air flow from the turbine inlet housing to the turbine inlet nozzle and control means associated with the air flow blocking means for controlling the operation of the blocking means.